Measurement of the pyroelectric coefficient and permittivity on Rhododendron and Encephalartos leaves and on the insect Periplaneta americana.

Pyroelectric (PE) voltage responses to single square radiation signals absorbed in epidermal layers of the leaves of Encephalartos villosus and Rhododendron catawbiense and in the integument of the insect Periplaneta americana L. were investigated on dry preparations as well as on whole fresh leaves and live insects. Measurements of the initial slopes of the responses, the rise times, and the peak voltages were carried out with 10 interchangeable load resistors from 5M omega to 10 G omega, connected parallel to the samples. In encephalartos leaves this yielded for the permittivity epsilon and the PE coefficient lambda in the upper/lower epidermis, epsilon = 30/60 and lambda = 2/6 pC/cm2K, respectively, and in rhododendron, epsilon = 60/200 and lambda = 3/15 pC/cm2K. In periplaneta we found epsilon = 300 and lambda = 20 pC/cm2K for the abdomen rings, and epsilon = 1,000 and lambda = 350 pC/cm2K for the thorax of live insects. Generally, dry preparations of leaves, and especially of insects, showed smaller PE responses. The outer epidermis of live plant leaves and the integument of live insects appear to be polar and to exhibit pronounced PE properties.